[PyQt] Subclass of QGraphicsObject does not have the correct class name listed in QGraphicsScene.items()

[Luke Campagnola]

Great,
Thanks Phil!

On Wed, Dec 7, 2011 at 07:56, Phil Thompson <phil at riverbankcomputing.com> wrote:
> On Mon, 5 Dec 2011 18:01:25 -0500, Luke Campagnola
> <lcampagn at email.unc.edu>
> wrote:
>> How about this:
>>
>> from PyQt4 import QtCore, QtGui
>> import sip
>> class GObject(QtGui.QGraphicsObject):
>>     def boundingRect(self):
>>         return QtCore.QRectF(0, 0, 10, 10)
>>     def paint(self, p, *args):
>>         p.drawRect(self.boundingRect())
>>
>> app = QtGui.QApplication([])
>> scene = QtGui.QGraphicsScene()
>> obj = GObject()
>> scene.addItem(obj)
>> items = scene.items(QtCore.QPointF(0,0))
>> objAddr = sip.unwrapinstance(sip.cast(obj, QtGui.QGraphicsItem))
>> itemAddr = sip.unwrapinstance(sip.cast(items[0], QtGui.QGraphicsItem))
>> print "Adresses match:", objAddr == itemAddr
>> print "QGraphicsObject matches:", obj is items[0]
>
>
> That turned out to be easier than I thought - thanks for making me look at
> it in a different way.
>
> Try current SIP hg or tonight's snapshot.
>
> Phil
>
>
>> On Mon, Dec 5, 2011 at 16:33, Phil Thompson
> <phil at riverbankcomputing.com>
>> wrote:
>>> On Mon, 5 Dec 2011 12:24:57 -0500, Luke Campagnola
>>> <lcampagn at email.unc.edu>
>>> wrote:
>>>> Howdy Phil,
>>>> I'm running into this issue where QGraphicsScene.items() does not
>>>> return the correct python objects if the items are subclassed from
>>>> QGraphicsObject. Your response to this issue several months ago was:
>>>>
>>>> On Fri, May 20, 2011 at 11:46, Phil Thompson
>>>> <phil at riverbankcomputing.com> wrote:
>>>>> It's because QGraphicsObject inherits both QObject and QGraphicsItem.
>>>>> items() returns a list of QGraphicsItems which, for a
> QGraphicsObject,
>>>>> has
>>>>> a different C++ address than the original QGraphicsObject. PyQt
> doesn't
>>>>> recognise that the QGraphicsItem is a cast of the QGraphicsObject. I
>>>>> don't
>>>>> think there is anything I can (sensibly) do about this.
>>>>
>>>> The workaround I am using for this bug is to maintain a dictionary
>>>> that maps from the QtGui::QGraphicsItem memory address back to the
>>>> original python object. Looks something like:
>>>>     cache[ sip.unwrapinstance(sip.cast(item, QtGui.QGraphicsItem)) ] =
>>> item
>>>>
>>>> This works, but it's rather messy since every instance of
>>>> QGraphicsObject and QGraphicsWidget needs to register itself with this
>>>> cache. I presume PyQt already maintains a similar dictionary so that
>>>> it can translate between Qt's internal memory addresses and PyQt's
>>>> wrapper objects. Would it not be straightforward to implement my
>>>> workaround from within PyQt?
>>>
>>> Not straightforward, but certainly worth thinking about.
>>>
>>> Do you have something small I can use as a test case?
>>>
>>> Phil